BIO 111 population ecology

what does population ecology focus on

groups of interbreeding individuals of one species

what is the main goal of population ecology

to understand factors affecting population growth, density, and size using demographic tools

what are quadrats and line transects used for

sessile non moving species like plants

what is a quadrat

-A quadrat is a square frame enclosing a known area. A quadrat can be used to sample plants or animals that don't move much.

what is a line transect

Marking a line along the ground between two poles and taking samples at specified points

what are tools used to study mobile species

traps like pitfall traps, mist nets, and live traps

what method is used to avoid counting the same individual more than once

mark-recapture method

what is necessary to fully understand population size changes

studying species interactions

how are animals marked in the mark recapture method

with a tag or other system so they can be recognized when recaptured

formula for total population size N

(number marked in first catch X total number in second catch) / number of marked recaptures in second catch

what assumption does the mark recapture method make about the population

that there is no migration, no births, or deaths between samplings

what does trap happy or trap shy mean

more or less likely to be attracted to traps

what are less invasive sampling methods

◦Radio collars

◦Drone

◦Pelt records from trading stations

◦Catch per unit effort

◦Counting fecal pellets, singing individuals, or leaf damage

what are dispersion patterns

the way individuals are spaced within a habitat.

why is it important to consider dispersion patterns in ecology studies

Will affect where you trap and how accurate your data

examples:

- clumped(schools of fish)

- uniform (penguins)

- random (wildflowers)

what does demography study

Looks at several characteristics of a population to make predictions about how it may change

why is demography important for conservation biologist

Essential for conservation biologists planning how to manage endangered species

- also city planners and urban developers

what is survivorship

the chance an individual will live to a certain age

what is a type I survivorship curve

most individuals die in late life

what is type 2 survivorship curve

uniform rate of decline

What is a type 3 survivorship curve?

huge decline in young

what is semelparity

all offspring produced in a single event, then usually adults die

◦Salmon spawning

what is iteroparity

repeated reproduction at intervals throughout the life cycle, seasonal or continuous

Many vertebrates, perennial plants, us

what can population age structure help predict

future population size

what does current human population growth depend on

the birth rate from 15-30 years ago

why is the birth rate from 15-30 years ago important

because that's when todays child bearers were born

what do age structure diagrams show

the distribution of population across age groups

how is population growth calculated

by subtracting the number of deaths from the number of births per unit of time

what happens if the birth rate is greater than the death rate

the population is growing

what happens if the birth rate is less than the death rate

the population is shrinking

what does the net reproductive rate represent

the average number of offspring an individual is expected to produce over its lifetime

net reproductive rate

what are the two simple models for population growth

exponential growth and logistic growth

what is exponential growth

◦resources not limiting, prodigious growth, can happen after species reintroduction

what is logistic growth

resources are limiting, limits the amount of growth

what type of growth do populations with unlimited resources follow initially

exponential growth

what are examples of limiting factors that stop population growth

disease, predators, and limited resources

what is carrying capacity

The maximum stable population size of a species that an ecosystem can support

what are the two broad categories of limiting factors

density dependent and density independent

what are density dependent factors

limitingfactors whose influenceis affected by population density.

◦Competition, disease, predators, parasites

what are density independent factors

unrelatedto population density.

◦Weather, environmental disturbance

what are two life history strategies in population ecology

r and K selected species

are species strictly r or K selected

no, most species fall somewhere on a spectrum between the two

what are the characteristics of r selected species

•high rate of per capita population growth (r), but poor competitive ability

◦Grow quickly and reach reproductive age early

◦Examples: weeds, insects

what are the characteristics of k selected species

•stable populations adapted to exist at or near carrying capacity, K

◦Devote energy to growth and maintenance, eventually outcompete r selected

◦Examples: trees, elephants

◦Vulnerable in a human-dominated world

why is human population growth unique

Unlike nearly every natural population, humans have demonstrated exponential growth, especially over the last 250 years.

what are interspecific interactions

relationships between species in a community

how are interspecific interactions classified

whether they help, harm, or have no effect on the species involved

examples of interspecific interactions

◦Competition, predation, herbivory, symbiosis (parasitism, mutualism, and commensalism), and facilitation

◦Can be positive (+), negative (-), or no effect (0)

All of these have led to evolutionary adaptations in both sides of the relationship

what is intrAspecific competition

competition between members of the same species

ex:

- exploitation: each caterpillar chews as much leaf as it can

- interference: each caterpillar physically intimidates one another

what is intErspecific competition

competition between different species

ex:

- exploitation: aphids and caterpillars compete for common resources

- interference: beetle and caterpillar use physical intimidation

what did joseph connells 1983 review find

competition was present in 55% of 215 species studied

what happens when single pairs of species use the same resource

◦competition is almost always reported (90%)

Frequency of competition varies with the number of species involved

why do plants show a high degree of competition

they cant move and may use allelopathy (chemical inhibition of other plants)

why do marine organisms tend to compete more than terrestrial organisms

space (on rocks in intertidal zones) is very limited

what did Gause's study conclude about species and niche's

Species with the same requirements cannot live together in the same place with the same resources - they cannot occupy the same niche

what is the competitive exclusion principle

Complete competitors cannot coexist unless they occupy different niches

what is resource partitioning

◦Describes differentiation of a niche in space and time

how can species reduce competition besides resource partitioning

diverge morphologically to use different resources in character displacement

character displacement in galapagos finches

what are two main ways to classify types of predation

◦How lethal they are for the prey

◦Length of association between consumer and prey

do predator defenses always protect prey populations

predators still succeed in taking down prey and controlling populations

- never ending evolutionary arms race

what are the two main types of anti predator defenses in plants

physical defenses (rose thorns) and secondary metabolites (chemical compounds produced by plants such as alkaloids in tobacco)

how does ecology set the stage for evolution

creating selective pressures that drive the development of plant defenses over time

how do herbivores overcome plant chemical defenses

by detoxifying the compounds using two main pathways

what is oxidation in the context of plant resistance

◦catalysis of secondary metabolite to corresponding alcohol by mixed-function oxidases (M F Os)

Occurs in the liver of mammals and midgut of insects

what is conjugation

unites results of oxidation with another molecule to create inactive and readily excreted product

what is parasitism

a relationship where one organism feeds off another without usually killing it

what is the organism being fed on in the parasitism called

the host

how can parasites vary in their relationship with the host

•Feed on one species or many

•Live entirely within host or release infective juveniles out

•Be internal or external

do all parasites leave their host

no, some parasites remain attached to the host for most of their life

what is an example of a parasite with a complex life cycle involving multiple host

plasmodium; parasite that causes malaria

how can some parasites increase their chances of transmission

by altering the behavior of the host

ex:

-cordyceps fungi (takes over insect behavior)

-toxoplasmosis (can alter behavior in rodents and 60 million Americans)

what is mutualism

Close associations between species in which both species benefit

◦Pollination systems

what is commensalism

One member derives a benefit while the other is unaffected

◦Seed dispersal via hooks or barbs

•Epiphytes growing in trees do not harm the trees

•Cattle egrets benefit from cattle stirring up insects

what is resource based mutualism

Both species receive a benefit in the form of resources

Leaf-cutting ants that farm fungus

what is defensive mutualism

One species receives food or shelter for defense

Ants protect aphid, aphid secretes honeydew. Ants defend the tree and trim away competing plants

what is dispersive mutualism

Species receives food in return for transporting pollen or seeds

what factors are most important in affecting population size

bottom up or top down factors

what do bottom up factors emphasize

•Plant quality and abundance control herbivores and the predators that feed on them

what do top down factors emphasize

•Predators and parasites control herbivore or plant prey

•Trophic cascade -effects cascade down to all feeding levels of a system

what are the two lines of evidence that food limitation controls population size

•Thermodynamic properties of energy transfer

•Nitrogen-limitation hypothesis

what does the nitrogen limitation hypothesis state

Organisms select food in terms of nitrogen content

•Animal tissue generally contains 10 times the amount of nitrogen in plant tissue

•Increasing supply of nitrogen to plants increases herbivore population size, survivorship, growth and fecundity

what does top down control suggest and what do predators vs. herbivores control

Suggests that natural enemies influence population densities

•Predators control prey populations (herbivores)

•Herbivores control plant populations

what studies support top down control and what is an example in the U.S.

•Evidence from studies of top predator removal and addition

•Example: Wolf reintroductions in the United States